Try Teignbridge Propellors. They are not generally expensive and do calculations on the phone.
I found my prop (new last year) over pitched and had a firm in Brixham flatten it out a bit - they did a nice job too.
We are going through the same process for a 3 blader for a new engine in our motor sailer. We did a lot of asking, then ended up with some excellent advice and sensible prices from C & O Engineering ( in the Newton Abbot area) Tel 01626 368872. I spoke to Graham.
Martin from C&O Engineering Newton Abbot.01626 367782
we have large selection of props in stock for quick delivery
we can also do prop caculation whilst you are on the phone to us